雄性布氏田鼠性腺发育的季节模式特征及其光响应分子机制

Excessive multiplication is one of important reasons of pest rodent breakout and, hence, the primary task for rodent management is to reveal the reproductive regulation. Seasonal breeding acts as the most important survival strategy in many rodents and reflects the adaption of animals to environment annual changes. Seasonal breeding is regulated by a series of factors, such as annual cycle of day-length (photoperiod), melatonin secreted from pineal gland and photoresponse genes (Dio2/3) from environment to gene level. Brandt's vole, a seasonal breeder, is the one of main pest rodent distributed in Inner Mongolia steppes. In our previous studies, we found that gonadal weights of male voles and day-length have the similar annual changes, which is caused by that newborn voles replace overwinter one to occupy the major of whole population and the differentiation of gonadal development pattern in different age group. Thus, we hypothesize that Brandt's voles have a physiological mechanism, like biological clock, by which the direction of gonadal development is determined by the phasic in annual cycle of day-length before or after they born. In this study, we will reveal the annual changes of male gonad and the expression level of photoresponse genes in wild and laboratory males born in spring and autumn; and then will test the effects of photoperiod, melatonin and photoresponse genes on the gonadal development of male voles born in early and later breeding season; and finally will find the relationship between DNA methylation and the expression and silence of photoresponse genes in gonadal development of both male groups. We aim to clarify the mechanisms of seasonal breeding in male Brandt's voles and provide theoretical basis for the management of rodents.

过度繁殖是害鼠种群暴发与成灾的重要原因，揭示鼠类繁殖规律是鼠害治理的首要任务。日照时长（光周期）是哺乳动物季节性繁殖的重要参照信号，Dio2/3则是动物体内传递光周期信号的重要调控基因。布氏田鼠是我国内蒙草原主要害鼠，具有明显的季节性繁殖现象。项目组前期研究发现，雄鼠性腺大小与日照时长的季节变化一致，相同年龄雄鼠的性腺大小在不同季节差异很大，但却都保持了年度周期性特征。我们推测布氏田鼠体内已形成响应日照时长年度相位的神经内分泌调控机制，决定出生于不同繁殖时期雄鼠性腺的季节发育模式。本研究通过分析不同时期出生雄鼠的性腺发育模式和光响应基因表达量，及其与光周期相位季节变化的相互关系，结合光控实验和激素处理实验及基因启动子甲基化分析，从环境、生理和分子水平分析验证布氏田鼠季节性繁殖的光响应调控机制。本项目将阐明布氏田鼠繁殖策略形成过程中环境和基因调控的作用机制，这也将为害鼠综合治理提供理论依据。

过度繁殖是害鼠种群暴发与成灾的重要原因，揭示鼠类繁殖规律是鼠害治理的重要任务。在前期研究的基础上，我们推测布氏田鼠具有响应日照时长年度相位的神经内分泌调控机制，决定着出生于不同季节个体的性腺发育模式。本研究通过野外自然种群和室内控制实验，来验证光周期是否可以改变布氏田鼠性腺发育，并寻找控制性腺发育的关键基因及可能的表观遗传学机制。主要结论如下：1）野外实验表明，不同季节雄鼠下丘脑Dio2和Dio3基因表现出与日照时长年度变化强烈的相关性，而Rfrp-3、Kiss-1和GnRH基因表现出显著的年龄差异，推测这些基因可能是在解析日照时长和调控性腺发育中起着关键作用；2）室内光周期处理结果表明，（渐）短光照对幼鼠性腺发育起抑制作用，而（渐）长光照则起促进作用；幼鼠对光周期的刺激或抑制作用敏感，而成鼠则消失；3）基因表达分析表明，渐短光照在抑制子代性腺发育的同时，上调下丘脑Dio3基因表达，说明该基因可能在解析季节光信号中具有重要作用；4）褪黑素注射抑制子代雄鼠性腺发育，同时改变下丘脑Dio2和Dio3基因的表达，进一步证明了这两个基因在解析褪黑素信号中具有重要作用；5）Dio2和Dio3基因启动子区的甲基化水平并未表现出与表达量之间明确关系，这说明甲基化作用可能不是调节这两基因表达量变化的主要机制。本研究发现夏至点附近是布氏田鼠性腺由活跃向抑制转变的关键时期；幼鼠和成体对光周期的敏感性不同；每天50μg褪黑素注射可显著抑制幼鼠的性腺发育；Dio2和Dio3基因对光周期相位和褪黑素注射均反应敏感，但表现出季节性差异，说明二者在布氏田鼠解析光周期季节信号中可能起到关键作用。本研究结果建立了布氏田鼠“（渐）短光照性腺抑制模型”和“褪黑素性腺抑制模型”，并验证了“光周期-褪黑素-下丘脑Dio2 & Dio3”通路在布氏田鼠解析季节性光周期信号和调节性腺发育中起到关键作用。这些结果为下一步筛选布氏田鼠性腺发育调控关键基因和解析鼠类繁殖调控机制提供了良好的模型基础和证据支持。